Method for manufacturing a ball cage of a joint

ABSTRACT

A method for manufacturing a ball cage of a joint, comprising an inner side, an outer side and windows between the inner side and the outer side, is provided, wherein a blank is clamped on a workpiece fixture of a machine tool, with a clamping area of the blank lying outside of a machining area, and wherein the inner side, the outer side and the windows are machined by the same machine tool without reclamping the workpiece.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT Application No. PCT/EP2008/060327, filed Aug. 6, 2008, and also claims the benefit of German Application No. 10 2007 043 746.5, filed Sep. 4, 2007, both of which are incorporated herein by reference in their entirety and for all purposes.

BACKGROUND OF THE INVENTION

The invention relates to a method for manufacturing a ball cage of a joint, which comprises an inner side, an outer side and windows between the inner side and the outer side. Ball cages are parts of joints such as, for example, homokinetic joints, which serve to hold balls between a ball socket and an inner star.

A multiple spindle machine tool is known from WO 2004/012888 A1, which comprises a machine frame, a first spindle slide with a first workpiece spindle and a second spindle slide with a second workpiece spindle, the first spindle slide and the second spindle slide being guided for linear displacement on the machine frame. Also provided is a tool receiving device. Arranged on the machine frame are a first guide and a spaced second guide, on which both the first spindle slide and the second spindle slide are guided. The first workpiece spindle and the second workpiece spindle are arranged between the two guides.

The machine tool described in this publication is, in principle, suited for performing the method according to the invention.

A method for producing profiled tracks for joint parts is known from WO 2005/089992 A1, wherein a cutting tool acts on the workpiece. Workpiece machining is performed with the cutting tool during the relative forward movement between workpiece and tool, and workpiece machining is performed with the same cutting tool during return movement following the forward movement.

A method of producing a ball cage for a constant-velocity universal joint is known from DE 10 2005 059 696 A1, which comprises an outer joint part with an internally cylindrical guiding face and an inner joint part with an outer spherical guiding face, and torque-transmitting balls held in the ball cage. A preformed annular blank with an outer face, an inner face, a first end face and a second end face is provided, the outer face comprising a spherical face and a conical face. Soft machining of the conical face is performed to produce a conical free face, with the spherical face initially remaining unmachined. The soft machined component is then hardened. Hard machining of the spherical face is performed to produce a control face, with the conical free face remaining unmachined.

A method for turning and finishing a workpiece is known from DE 10 2005 015 649 A1, wherein a workpiece carrier removes the workpiece from a conveying device and clamps it for turning, during which the geometry of the workpiece is turned to size and shape, and the workpiece is placed on the conveying device again after completion of the machining. A finishing device is provided, and the turning and finishing are performed during the same clamping.

A method for machining hubs of homokinetic joints is known from DE 100 56 132 C2, wherein both the outer contour serving as cage track and the ball tracks are machined by chip removal. The machining of the outer contour and the machining of the ball tracks are performed during an unchanged clamping of the workpiece, and the machining of the ball tracks is performed by a disc-shaped tool which has an axis of rotation extending perpendicularly to the ball track and the diameter of which is a multiple of the width of the ball track.

A method of finishing hardened ball cages for constant-velocity joints that are provided with inner and outer ball race-shaped bearing surfaces and ball pockets for accommodating torque-transmitting balls is known from EP 0 952 364 B2. Hard turning of the ball cage is performed to form the inner ball race-shaped bearing surface, an end contact surface and two annular cylindrical clamping surfaces defining the inner bearing surface. The ball cage is reclamped by means of the cylindrical clamping surfaces and the end contact surface, and hard turning of the ball cage is performed to form the outer ball race-shaped bearing surface and contact surfaces to be formed in the ball pockets for one ball each, which face one another in the axial direction.

SUMMARY OF THE INVENTION

In accordance with the present invention, a manufacturing method is provided, with which ball cages of high workpiece quality can be effectively produced.

In an embodiment of the manufacturing method according to the invention, a blank is clamped on a workpiece fixture of a machine tool, with a clamping area of the blank lying outside of a machining area, and the inner side, the outer side and the windows are machined by the same machine tool without reclamping the workpiece.

In the solution according to the invention, a complete machining of the ball cage is performed on the same machine tool. There is no reclamping of the workpiece for the individual machining steps. Reclamping operations basically lead to different deformation of a workpiece and, consequently, to the occurrence of different states of tension. This may result in a decrease in the workpiece quality. In the solution according to the invention, the machining is performed during one clamping, whereby the workpiece quality is increased.

Furthermore, the complete machining is preferably performed on a single machine tool. The manufacture can thereby be performed effectively. For example, it is no longer necessary to machine an abutment surface which serves as reference for different machining methods. A machine reference (“software reference”) is defined by the clamping in a single workpiece fixture without reclamping.

Ball cages of high workpiece quality can be manufactured with minimization of time and costs by the method according to the invention.

In particular, the clamping area is an area outside of areas of contact of the ball cage with other joint parts. Consequently, machining of this clamping area is no longer necessary.

Ball cages usually have an annular area or cylinder area which is suited as clamping area.

In particular, the workpiece is held clamped at the clamping area by the workpiece fixture. An axial stop position for defining an axial reference is thereby also obtained.

It is quite particularly advantageous for the workpiece to be held with a set clamping force on the workpiece fixture. Optimized machining possibilities are thereby achieved and high workpiece qualities are obtained.

Provision is made for the clamping force to be set such that the workpiece is secured against rotation under the forces that occur, such that no workpiece vibrations occur, and such that the workpiece does not undergo deformation, in particular, compression, as a result of the clamping. This is an optimization process which must take counteractive effects into consideration. The more firmly a workpiece is clamped, the lower are the workpiece vibrations and the more securely is it held against rotation. Too strong a clamping force can, however, cause a deformation and, consequently, an impairment of the workpiece quality. An optimization process can be performed here by a controlled setting of the clamping force.

It is expedient for clamping surfaces for clamping the workpiece to be manufactured with increased static friction. A secure holding of the workpiece against rotation with minimization of workpiece deformation is thereby achieved.

An increased adhesive force is, for example, achieved by clamping surfaces of the workpiece fixture and/or of the workpiece being coated with a material having a high static friction.

Alternatively or additionally, it is possible for clamping surfaces (of the workpiece and/or of the workpiece fixture) to be roughened by, for example, sandblasting.

In an embodiment, it is provided that the blank is a hardened blank. A complete machining (final machining) for manufacturing the ball cage can then be performed by hard fine machining. It can, therefore, be manufactured with time- and cost-efficiency. Upon leaving the machine tool, the workpiece is completely machined and usable.

In particular, hard fine machining is then performed on the machine tool without reclamping. Complete machining is performed without any reclamping operations.

It is expedient for the machining of the inner side to be performed by grinding and/or turning (by a lathe) and, in particular, hard turning, on a lathe. A high surface quality is thereby effectively achieved on the inner side of the ball cage.

For the same reason, it is expedient for the machining of the outer side to be performed by grinding and/or turning and, in particular, hard turning, on a lathe.

It is possible for the machining of the inner side and the machining of the outer side to be performed simultaneously or successively. In principle, the sequence of the machining of the inner side and the machining of the outer side is optional.

In an embodiment, the machining of the inner side and the machining of the outer side are performed with the same tool. The time required for the machining is thereby optimized as there is no need to reclamp the tool.

In particular, the tool has a first cutter for the machining of the inner side and a second cutter for the machining of the outer side. Both the machining of the inner side and the machining of the outer side can, therefore, be performed with the same tool. In particular, the first cutter and the second cutter are offset from each other with respect to height and are also offset from each other transversely to the height direction. Therefore, the second cutter does not impede the machining of the inner side.

The tool is constructed so as to enable the first cutter to enter an inner space of the ball cage up to a maximum depth of entry without any further area of the tool touching the workpiece or a workpiece fixture. With appropriate adaptation to shape, the same tool can, therefore, be used for both the machining of the inner side and the machining of the outer side.

It is, in principle, also possible for the machining of the inner side and the machining of the outer side to be performed with different tools.

In an embodiment, the tool is held in a rotationally fixed manner and the workpiece is rotated during the machining of the inner side and the machining of the outer side. The workpiece is thereby machined by turning.

It may be provided that the workpiece fixture is arranged on a workpiece spindle which is displaceable in at least one direction. This results in optimized machining possibilities.

It is expedient for the workpiece spindle to be a vertical spindle having a longitudinal axis which is vertically orientated in relation to the direction of gravity. This results in an optimized discharge of chips, and it is, for example, possible to carry out dry machining.

It is then expedient for the workpiece spindle to be displaceable in the vertical direction. A displacement movement between the tool and the workpiece is thereby enabled, in order, for example, to introduce a tool into an inner space of the workpiece.

It may be provided that the workpiece and a tool are displaceable relative to each other in at least one horizontal direction in relation to the direction of gravity. For example, the workpiece is displaceable by means of a corresponding workpiece spindle in an X-direction perpendicularly to a vertical Z-direction, and one or more tools are displaceable in a Y-direction perpendicularly to the X-direction and to the Z-direction. This results in extensive machining possibilities. For example, the workpiece can be machined by turning by displacement in X-direction and Z-direction. An effective window machining can be performed by displacement in Y-direction.

It is expedient for the machining of the workpiece to be performed as dry machining. With effective performance of the method, this results in optimized workpiece qualities.

In principle, whether the machining of the windows is performed after the machining of the inner side or the machining of the outer side is optional. In order to prevent burrs on the manufactured component, it is expedient for the machining of the windows to be performed before the machining of the inner side and the machining of the outer side.

It is expedient for machining of the windows to be performed by milling and/or grinding. An optimized surface quality is thereby obtained in the area of places in contact with balls.

It may be provided that a tool and the workpiece are rotated during the machining of the windows. In particular, the tool is rotated. The workpiece may also be rotated (the machining operation is then, in particular, a rotary milling operation) or rotated or pivoted within a finite angular range.

In an embodiment, an axis of rotation of the tool and an axis of rotation of the workpiece extend parallel to each other. In particular, the workpiece is rotated and the tool is rotated.

It is then provided that the tool is rotated n times faster than the workpiece if the workpiece has n windows. A synchronization of the tool with the workpiece with respect to the windows to be machined is thereby obtained.

It is also possible for an axis of rotation of the tool and an axis of rotation of the workpiece to extend perpendicularly to each other. In particular, a machining during which the tool is rotated and the workpiece is only rotated or pivoted within a finite angular range is then performed.

It is also possible for the workpiece to be linearly displaced relative to the tool in a direction parallel to an axis of rotation of the tool during the machining of the windows. In particular, the workpiece is then not rotated.

It may be provided that the blank on which the manufacturing method according to the invention is based is made from a tube which is rolled and turned on an inner side, and from which windows are punched out. The aforementioned machining operations are, in particular, soft machining operations.

It may be provided that the blank is hardened prior to clamping on the machine tool. Hard machining operations are then performed on the machine tool.

The following description of preferred embodiments serves in conjunction with the drawings to explain the invention in greater detail.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to assist the understanding of certain embodiments of the invention, reference will now be made to the appended drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 shows a diagrammatic representation of an embodiment of a machine tool on which the method according to the invention is performable;

FIG. 2 shows a diagrammatic representation of steps for performing the method according to the invention;

FIGS. 3( a) and (b) show a diagrammatic representation of a first embodiment for window machining, wherein FIG. 3( a) shows diagrammatically a side view of the workpiece machining and FIG. 3( b) is a sectional view taken along line b-b in FIG. 3( a);

FIGS. 4( a) and (b) show diagrammatically a second embodiment for window machining, wherein FIG. 4( a) shows diagrammatically a side view of the workpiece machining and FIG. 4( b) is a sectional view taken along line b-b in FIG. 4( a);

FIGS. 5( a) and (b) show diagrammatically a third embodiment for window machining, wherein FIG. 5( a) shows diagrammatically a side view of the workpiece machining and FIG. 5( b) is a sectional view taken along line b-b in FIG. 5( a);

FIG. 6 shows a diagrammatic representation of a tool for machining the inner side and for machining the outer side;

FIGS. 7( a) to (e) show diagrammatically various intermediate steps for machining the inner side;

FIGS. 8( a) to (c) show various partial steps for machining the outer side; and

FIG. 9 shows a perspective representation of an embodiment of a homokinetic joint with a ball cage.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter. However, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. As used in this specification and the claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

An embodiment of a multiple spindle machine tool with which the method according to the invention is performable is denoted in its entirety by 10 in FIG. 1. It comprises a machine frame 12 by means of which the multiple spindle machine tool 10 (shown here as twin spindle machine tool) is positionable in alignment on a base. On the machine frame 12, a first spindle slide 14 is guided on a stand 13 for linear displacement in a direction X. This direction X is, in particular, a horizontal direction. It is orientated perpendicularly to the drawing plane in FIG. 1. The first spindle slide 14 carries a first workpiece spindle 16 on which a workpiece to be machined is rotatably fixable. The first workpiece spindle 16 is guided on the first spindle slide 14 for displacement in a transverse direction Z in relation to the direction X, so that the spacing of a workpiece held on the first workpiece spindle 16 can be set relative to the machine frame 12. An axis of rotation of the first workpiece spindle 16 about which a workpiece held thereon is rotatable extends parallel to the Z-direction.

Furthermore, a second spindle slide 18 is provided, which is also guided on the machine frame 12 for linear displacement in the X-direction. This second spindle slide 18 holds a second workpiece spindle 20, which is held on the second spindle slide 18 for linear displacement in the Z-direction.

The two workpiece spindles 16 and 20 are, in particular, aligned substantially parallel to each other.

A first drive 22 is provided for driving the first workpiece spindle 16 in its displacement movement along the Z axis. For example, this may be a hydraulic drive, a ball screw drive or a linear motor. A drive unit of the first drive 22 is seated on the first spindle slide 14 and is moved together with it in the X-direction.

For guiding the first workpiece spindle 16, the first spindle slide 14 has a guiding device denoted in its entirety by 24, on which the first workpiece spindle 16, driven by the first drive 22, is displaceable in the Z-direction. The Z-direction is, in particular, aligned vertically, i.e., parallel to the direction of gravity. The first workpiece spindle 16 and the second workpiece spindle 20 are then vertical spindles.

For moving the second workpiece spindle 20 relative to the second spindle slide 18, a second drive 26 is provided, which activates the linear displacement of the second workpiece spindle 20 on a guiding device 28 in the Z-direction relative to the second spindle slide 18.

At their lower ends, the workpiece spindles 16 and 20 are each provided with a workpiece holder 30, 32, on which the respective workpieces are fixable for rotation about longitudinal axes 34, 36 of the respective workpiece spindles 16, 20.

A tool receiving device 38 is arranged on the machine frame 12 for pivotal movement about an axis B. This pivot axis 40 is orientated transversely to the Z-direction and X-direction and is, in particular, horizontally aligned. In a twin spindle machine tool, the tool receiving device 38 comprises a first tool receiver 42 and a second tool receiver 44, which are spaced from each other. The tool receivers 42, 44 are seated on rotatably driven tool spindles 43, 45, so that the correspondingly held tools such as milling tools or drilling tools are rotatable about a spindle axis. Two workpieces can then be simultaneously machined by respective tools, with a first workpiece being held at the first workpiece spindle 16, and a second workpiece being held at the second workpiece spindle 20.

The two tool receivers 42 and 44 are seated on a yoke-shaped rocker arm 46, which is pivotable about the pivot axis 40 (B-axis). A drive 47 is provided for performing the pivotal movement. Each pivot position of the tool receiving device 38 is settable within a certain pivot range, so that in a specific set pivot position, the respective workpieces held on the workpiece spindles 16 and 20 can be machined by the tools fixed on the tool receiving device 38 and, in particular, present in the tool receivers 42, 44.

Furthermore, the tool receivers 42, 44 are displaceable in the Y-direction. For this purpose, the rocker arm 46 is held on a displaceable slide 49 which is guided for displacement on a guide device 51. The Y-direction extends perpendicular to the X-direction and Z-direction.

For example, it is thus possible to produce a constant velocity joint which comprises ball tracks in an axle journal and in a hub (cf. WO 2005/089992 A1).

In particular, it is possible to perform soft milling, grinding or hard milling operations using suitable tools. Hard turning operations can also be performed.

For this purpose, suitable additional devices, such as, for example, one or more rotary consoles with a suitable turning tool or additional spindles are provided, which are arranged in the region of the machining zone of the workpieces (not shown in the drawing).

It is also possible to carry out subsequent machining on a workpiece by, for example, it being first held at the first workpiece spindle 16 and machined by a first tool and subsequently transferred to the workpiece spindle 20 and then machined by a second tool.

A pivot space 48 is formed at the machine frame 12 to enable the tool receiving device 38 to pivot unobstructed within a certain pivot range on the machine frame 12. Also, chips and the like can be discharged through this pivot space 48.

In relation to the Z-direction, the spindle slides 14 and 18 are guided so as to be displaceable above the tool receiving device 38 in the X-direction. For this purpose, a first guide 50 is provided, which, in particular, comprises a guiding rail which is arranged at a spacing from the tool receiving device 38 above it. Furthermore, a second guide 52 is provided, which is arranged at a parallel spacing from the first guide 50, in particular, at the same level as the first guide 50 in the Z-direction above the tool receiving device 38. The second guide 52, in particular, again comprises a guiding rail. In particular, the two guides 50 and 52 are arranged horizontally. The guides 50, 52 are seated on the stand 13.

The guides 50, 52 can also be arranged so as to be offset in the Z-direction in order, for example, to be able to additionally reinforce a spindle slide in the direction of its height, should this be necessary.

In its region facing the guides 50, 52, the first spindle slide 14 is designed so as to be L-shaped or triangular and so as to comprise a first leg which is orientated along the first guide 50 and guided thereon. For example, two spaced guiding shoes are provided in order to guide the first leg for linear displacement on the first guide 50. The first leg is connected to a second leg which is orientated transversely to the first leg and which is coupled to the second guide 52, for example, by means of a guiding shoe in order to guide the second leg for linear displacement on the second guide 52.

Between and at the two legs, the first workpiece spindle 16 is positioned between the two guides 50 and 52.

The face of contact of the first spindle slide 14 with the first guide 50, for linearly displaceable coupling thereto, is greater than the face of contact for coupling to the second guide 52. For example, the first face of contact is formed by the two guiding shoes, whereas for the second guide 52 the face of contact is formed by the one guiding shoe only.

The second spindle slide 18 also comprises a first leg which is orientated along the second guide 52 and, for example, coupled thereto by two guiding shoes. A second leg which is coupled to the first guide 50 by a guiding shoe is arranged transversely to this first leg. Therefore, the second spindle slide 18, too, has an L-shaped or triangular outer shape, with the face of contact in contact with the second guide 52 being greater than the face of contact with the first guide 50. The second workpiece spindle 20 is seated between the first leg and the second leg at these and between the two guides 50 and 52 and faces the other workpiece spindle 16, with a free intermediate region remaining between the two workpiece spindles 16, 20.

The L-shaped or triangular shape refers to a cross section in a projection onto the plane formed by the two guides 50 and 52, at least in the region where the spindle slides 14 and 18 are coupled to these guides 50 and 52, respectively.

Such a multiple spindle machine tool is described in WO 2004/012888 A1,

US 2005/0139048 A1 and U.S. Pat. No. 7,124,666. These applications/documents are incorporated herein and made a part hereof by reference.

The machine tool 10 comprises a control device 54 for controlling the movements and positions of the machine elements. The method according to the invention can be performed using the control device 54.

An embodiment of a joint and, in particular, a homokinetic joint, which is shown in a (partial) exploded representation in FIG. 9 and is denoted by 56, comprises a ball star 58 with ball tracks 60. When in use, the ball star 58 is rotationally fixedly connected to a drive shaft.

The joint 56 further comprises a ball socket 62 in the shape of a bell. Ball tracks 64 are also formed in this. When in use, the ball socket 62 is rotationally fixedly connected to a wheel.

Arranged between the ball socket 62 and the ball star 58 is a ball cage 66. This ensures that the balls (not shown in FIG. 9) are held. The balls enable the joint 56 to ensure a uniform (homokinetic) transfer in the case of flexing angles up to a limit angle.

The balls run on the ball tracks 60 and 64 and contact parts of the ball cage 66. The corresponding surfaces must be of high-quality construction.

The ball cage 66 has an outer side 68, an inner side 70 delimiting an inner space 72 in which the ball star 58 is positioned, and windows 74 between the inner side 70 and the outer side 68.

The method according to the invention for manufacturing a ball cage relates to the fine machining and, therefore, final machining of a ball cage.

The starting point for the manufacturing method according to the invention is a ball cage blank which is produced by soft machining. For example, such a ball cage blank is produced from a cut-off section of tube which is rolled and turned on the inner side. Windows are produced in this blank by punching. Hardening then takes place. The manufacturing method according to the invention is performed on such a hardened blank. (Alternatively, the manufacturing method according to the invention is performed before the hardening.)

The manufacturing method according to the invention is performed as follows. A hardened blank 76 (FIG. 2) is clamped on a workpiece fixture 78 of the workpiece holder 30 or 32. A clamping area 80 of the blank 76 is an annular area 82, also referred to as cylinder area, which is positioned at an end of the blank 76 and has a hollow-cylindrical interior 84. The clamping area 80 is arranged and constructed so as not to contact any other joint parts (i.e., not the ball socket 62 the ball star 58 or the balls) in a manufactured joint 56. There is then no necessity for any further machining of the clamping area 80.

The workpiece fixture 78 has a chuck 86 which presses on an inner side of the annular area 82. The blank 76 is thereby held clamped to the workpiece fixture 78. The corresponding tension force (clamping force) is set in a defined manner, namely such that the workpiece is held so as to be unable to rotate during the machining. Furthermore, the clamping force is set such that the workpiece does not undergo deformation and, in particular, is not crushed. The clamping force is also set so as to eliminate any vibrations of the workpiece during the machining.

The workpiece fixture 78 has an abutment area 88 of, for example, annular construction, on which an outer side of the blank 76 may be placed for axial positioning.

Measures may be taken for increasing the static friction between workpiece fixture 78 and blank 76. For example, clamping surfaces of the blank 76 and/or, in particular, of the workpiece fixture 78 are coated with a material which increases the static friction. It may also be provided that corresponding clamping surfaces are roughened, for example, by sandblasting, in order to increase the static friction.

The final machining of the workpiece is performed on the same machine tool 10, without the workpiece being released from the workpiece fixture 78. Complete machining is performed without reclamping. It is thereby ensured that, for example, an inner diameter, an outer diameter and a center line of the windows 74 match one another optimally. The running smoothness and the service life of a ball cage manufactured in accordance with the invention can be increased by the complete machining being performed during one clamping.

Only one machine tool is used for the complete machining of the workpiece in the manufacturing method according to the invention. Reclamping errors are eliminated. With each new clamping of a workpiece, it basically undergoes different deformation, and different states of tension occur in the workpiece. This may result in a reduction in the workpiece quality. The workpiece quality is improved by the machining of the workpiece with the manufacturing method according to the invention.

Furthermore, there is no necessity either for machining an abutment surface as reference surface for reclamping operations in the method according to the invention since the machining takes place during one clamping without any reclamping.

Hard fine machining with window machining (indicated by reference numeral 90 in FIG. 2), outer side machining (indicated by reference numeral 92 in FIG. 2) and inner side machining (indicated by reference numeral 94 in FIG. 2) is performed on the blank 76 in the machine tool 10. The window machining, outer side machining and inner side machining constitute the complete machining of the blank 76 to produce the ball cage 66 in its final form, with the necessary surface quality being produced at points that contact balls and at the other joint parts.

In principle, the sequence of the window machining, outer side machining and inner side machining is optional. It is preferable for the window machining to be performed first, and the outer side machining and/or inner side machining subsequently, in order to prevent burrs.

The hard fine machining of the windows is, in particular, a grinding operation or milling operation with one or more rotating milling tools. In a first embodiment, which is shown diagrammatically in FIG. 3 (a), the blank is rotated about an axis of rotation 96. The axis of rotation 96 coincides with the longitudinal axis 34 or 36 of the corresponding workpiece holder 30 or 32. In the embodiment in which the corresponding workpiece spindle is a vertical spindle, the axis of rotation 96 is a vertical axis.

A milling tool 98 with one or more corresponding cutters 100 rotates about an axis of rotation 102 which extends parallel to the axis of rotation 96. In this case, the angle in the B-axis B_(u) of the corresponding tool receiver 42 or 44 is zero degrees. In particular, the cutter 100 is configured as a fly cutter.

The rotation of the corresponding workpiece spindle 16 or 20 and of the corresponding tool spindle 43 or 45 is synchronized. The axes of rotation 96 and 102 are offset transversely to the direction of the axes. If the blank has n windows, the blank then rotates n times slower around the axis of rotation 96 than the milling tool 98, in order to enable machining of the windows as hard fine machining, i.e., f_(tool)=n·f_(w), where f_(tool) is the rotational frequency of the milling tool 98 and f_(w) the rotational frequency of the workpiece 76.

In FIG. 3( b), a machined window 104 is shown, and a milled profile is indicated by reference numeral 106. Also indicated is a track 108 of a corresponding cutter. The profile 106 is curved. The same profile can be produced on opposite flanks by corresponding forward and rearward turning.

The machining operation is a turn milling operation.

In a second embodiment shown in FIG. 4, an axis of rotation 110 of a corresponding tool 112 extends perpendicularly to an axis of rotation 114 of the workpiece 76. This is achieved by the rocker arm 46 being turned in relation to the starting position with B_(α)=0° through 90° to B_(α)=90°. The tool 112 is rotated about the axis of rotation 110. To machine the windows, the workpiece 76 is not rotated about the axis of rotation 114, but instead only pivoted through a finite angle of rotation.

A milled profile 107 (FIG. 4( b)), which is curved to a lesser extent than the milled profile 106, can be produced with this method.

In a third embodiment shown diagrammatically in FIG. 5, the tool 112 is again pivoted through 90° about the pivot axis 40, i.e., the angle B_(α)is 90°.

The workpiece 76 is not rotated. It is displaced in the Y-direction, and the tool 112 is displaced in the Y-direction. A milled profile 116 can thereby be produced, which is in parallel alignment with the Y-direction.

One or more of the methods described with reference to FIGS. 3 to 5 can be combined on a workpiece.

Complete machining of the windows is performed by one or more of the described partial steps.

The machining of the inner side and the machining of the outer side can take place simultaneously or successively using one or more tools.

In one embodiment, the machining of the inner side and the machining of the outer side are performed using a common tool 118 (FIG. 6). This tool is clamped on the corresponding tool receiver 42 or 44. It has a first cutter 120 for machining the inner side and a second cutter 122 for machining the outer side. The first cutter 120 and the second cutter 122 are spaced from each other in relation to a height axis 124, with the first cutter being located further towards the front. They are also spaced from each other in a direction transverse to the height axis 124.

An outer profile 126 of the tool 118 is so constructed that during the machining of the inner side by the first cutter 120 no other area of the tool 118 touches the workpiece. A recessed area 130 located below the first cutter 120 and above the second cutter 122 is correspondingly formed on a front side 128 of the tool 118. As will be described in further detail hereinbelow, this makes it possible to enter the inner space 72 of the ball cage to be manufactured.

The tool 118 has a shaft 132 for clamping it to the corresponding tool holder. The shaft 132 is constructed with a high degree of rigidity.

Partial steps for machining the inner side are indicated in FIGS. 7( a) to (e). This is a hard turning operation. The cutters 120 and 122 are turning tools.

Grinding tools may also be used.

The tool 118 is held in a rotationally fixed manner. The workpiece 76 is rotated about the axis of rotation 114. The first cutter 120 is made to enter by lowering the workpiece 76 by way of the Z-movability of the corresponding workpiece spindle. The grinding operation or hard turning operation can be performed on the inner side of the workpiece 76 by a synchronized X-movement of the corresponding workpiece spindle.

As will be apparent from FIGS. 7( d) and (e), the recessed area 130 on the outer profile 126 of the tool 118 enables the first cutter 120 to enter as far as the clamping area 80 without the outer profile 126 touching the workpiece.

After the hard fine machining by hard turning of the inner side, the outer side is also machined by hard turning. This is indicated in FIGS. 8( a) to (c).

The workpiece 76 is lowered by means of the corresponding workpiece spindle. The machining of the outer side is performed by corresponding X-Z-movement of the workpiece spindle. During this, the workpiece 76 is rotated about the axis of rotation 114, and the tool 118 is held in a rotationally fixed manner.

The recessed area 130 again makes is possible for the tool 118 not to touch the corresponding workpiece holder (for example, 30).

The outer profile 126 of the tool 118 is thereby adapted to the shape of the workpiece and to the shape of the workpiece holder.

The workpiece is lowered to such an extent that the entire outer side up to the clamping area is machined by hard turning using the tool 118 with the second cutter 122.

The machining of the inner side may also be performed after the machining of the outer side. If corresponding tools are used, it is, in principle, also possible for the machining of the inner side and the machining of the outer side to be performed simultaneously.

The result of the manufacturing method according to the invention is a ball cage which is completely machined and requires no finishing (such as grinding or the like). The hard fine machining is performed on a hardened blank without any reclamping.

In an embodiment of the method according to the invention, machining of the inner side, machining of the outer side and machining of the windows are performed by hard fine machining on a hardened blank. In particular, the machining of the inner side and the machining of the outer side are hard turning or grinding. The machining of the windows is a milling operation or grinding operation.

The machining is performed during one clamping. The elements of the ball cage can thereby be optimally matched in their tolerances. Clamping surfaces require no more machining. A high workpiece quality is obtained with effective time-saving machining.

The machine tool described in WO 2004/012888 A1, and the machine tool XG of Ex-Cell-O GmbH have a high machine rigidity and are, therefore, particularly well suited for performing the manufacturing method according to the invention.

The windows are machined in an interrupted cutting operation. As a result, high stimulation of vibrations may occur on the tool and the workpiece. This can be counteracted by vibration-damping measures on the machine tool, the tool and the workpiece fixture.

The cutting operation is preferably performed so as to avoid chip nests, in particular, at windows of the workpiece.

The workpiece may be machined in a dry state as a grinding operation on a supporting surface is no longer required.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing description. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

1. A method for manufacturing a ball cage of a joint, said ball cage comprising an inner side, an outer side and windows between the inner side and the outer side, comprising: clamping a blank on a workpiece fixture of a machine tool, with a clamping area of the blank lying outside of a machining area; and machining the inner side, the outer side and the windows by the same machine tool without reclamping the workpiece.
 2. The method in accordance with claim 1, wherein the clamping area is an area outside of areas of contact of the ball cage with other joint parts.
 3. The method in accordance with claim 1, wherein the clamping area is an annular area.
 4. The method in accordance with claim 1, wherein the workpiece is clamped at the clamping area by means of the workpiece fixture.
 5. The method in accordance with claim 1, wherein the workpiece is held with a set clamping force on the workpiece fixture.
 6. The method in accordance with claim 5, wherein the clamping force is set such that the workpiece is secured against rotation under the forces that occur, such that no workpiece vibrations occur, and such that the workpiece does not undergo deformation as a result of the clamping.
 7. The method in accordance with claim 1, wherein clamping surfaces for clamping the workpiece are manufactured with increased static friction.
 8. The method in accordance with claim 7, wherein clamping surfaces are coated in order that the static friction is increased.
 9. The method in accordance with claim 7, wherein clamping surfaces are roughened.
 10. The method in accordance with claim 1, wherein the blank is a hardened blank.
 11. The method in accordance with claim 10, wherein the machining of the blank is performed by hard fine machining.
 12. The method in accordance with claim 1, wherein the machining of the inner side is performed by at least one of grinding and turning.
 13. The method in accordance with claim 1, wherein the machining of the outer side is performed by at least one of grinding and turning.
 14. The method in accordance with claim 12, wherein at least one of the machining of the inner side and the machining of the outer side is performed by hard turning.
 15. The method in accordance with claim 1, wherein the machining of the inner side and the machining of the outer side are performed simultaneously or successively.
 16. The method in accordance with claim 1, wherein the machining of the inner side and the machining of the outer side are performed with the same tool.
 17. The method in accordance with claim 16, wherein the tool has a first cutter for the machining of the inner side and a second cutter for the machining of the outer side.
 18. The method in accordance with claim 17, wherein the first cutter and the second cutter are offset from each other with respect to height.
 19. The method in accordance with claim 17, wherein the tool is constructed so as to enable the first cutter to enter an inner space of the workpiece up to a maximum depth of entry without any further area of the tool touching the workpiece or a workpiece holder.
 20. The method in accordance with claim 1, wherein the machining of the inner side and the machining of the outer side are performed with different tools.
 21. The method in accordance with claim 1, wherein the tool is held in a rotationally fixed manner during the machining of the inner side and the machining of the outer side.
 22. The method in accordance with claim 1, wherein the workpiece fixture is arranged on a workpiece spindle which is displaceable in at least one direction.
 23. The method in accordance with claim 22, wherein the workpiece spindle is a vertical spindle.
 24. The method in accordance with claim 23, wherein the workpiece spindle is displaceable in the vertical direction.
 25. The method in accordance with claim 1, wherein the workpiece and a tool are displaceable relative to each other in at least one horizontal direction in relation to the direction of gravity.
 26. The method in accordance with claim 1, wherein the machining of the workpiece is performed as dry machining.
 27. The method in accordance with claim 1, wherein the machining of the inner side and the machining of the outer side are performed after the machining of the windows.
 28. The method in accordance with claim 1, wherein machining of the windows is performed by at least one of milling and grinding.
 29. The method in accordance with claim 1, wherein a tool and the workpiece are rotated during the machining of the windows.
 30. The method in accordance with claim 29, wherein an axis of rotation of the tool and an axis of rotation of the workpiece extend parallel to each other.
 31. The method in accordance with claim 29, wherein the tool is rotated n times faster than the workpiece if the workpiece has n windows.
 32. The method in accordance with claim 29, wherein an axis of rotation of the tool and an axis of rotation of the workpiece extend perpendicular to each other.
 33. The method in accordance with claim 1, wherein the workpiece is displaced linearly relative to the tool in a direction parallel to an axis of rotation of the tool during the machining of the windows.
 34. The method in accordance with claim 33, wherein the workpiece is held in a rotationally fixed manner.
 35. The method in accordance with claim 1, wherein the blank is made from a tube which is rolled and turned on an inner side, and from which windows are punched out.
 36. The method in accordance with claim 35, wherein the blank is hardened prior to clamping on the machine tool. 